Lead-free free-cutting aluminum brass alloy and its manufacturing method

Abstract

The present invention provides a lead-free free-cutting aluminum brass alloy and its manufacturing method. The alloy comprises: 57.0˜63.0 wt % Cu, 0.3˜0.7 wt % Al, 0.1˜0.5 wt % Bi, 0.2˜0.4 wt % Sn, 0.1˜0.5 wt % Si, 0.01˜0.15 wt % P, at least two elements selected from the group of 0.01-0.15 wt % Mg, 0.0016-0.0020 wt % B, and 0.001-0.05 wt % rare earth elements and the balance being Zn and unavoidable impurities. The inventive alloy has excellent castability, weldability, cuttability and corrosion resistance. It is suitable for low pressure die casting, gravity casting, horizontal continuous casting, forging and extrusion. Its metal material cost is lower than bismuth brass. It is particularly applicable for components used in drinking water supply systems and other structural components. It is a new environmentally-friendly free-cutting aluminum brass alloy.

Description

FIELD OF THE INVENTION[0001]The present invention generally relates to a lead-free free-cutting aluminum brass alloy, in particular a lead-free free-cutting aluminum brass alloy and its manufacturing method which is applicable in low pressure die castings and forgings.BACKGROUND OF THE INVENTION[0002]Currently, when people search and develop lead-free or low lead free-cutting brass alloys, they typically follow two routes to find the elements which could replace Lead: one route is to select the elements which hardly form solid solutions in Cu and can't form intermetallic compounds with Cu, such as Bi, Se and Te, etc; the other route is to select the elements which will form solid solutions in Cu wherein the solid solubility is reduced with decreasing temperature, so as to form intermetallic compounds with Cu, and with Sb, P, Mg, Si, B and Ca, etc. The first route has been well-known for some time. The second route is a more recent development.[0003]In the process of researching and ...

AI Technical Summary

Benefits of technology

[0039]Trace antimony can improve dezincification corrosion resistance of the alloy, like tin and arsenic. In the common casting copper alloys, the allowed iron content is larger than 0.2 wt %. In the inventive alloy, aluminum and silicon are present and iron will form hard-brittle iron-aluminum intermetallic compounds and iron silicide, which will decrease the plasticity, corrosion resistance and castability. In addition, if the hard particles formed by these intermetallic compounds are placed on the surface of the products, after polishing and electroplating, a “hard spots” defect characterized by inconsistent brightness will appear. Any such products must be scrapped.

[0024]In the inventive alloy, aluminum is the main alloy element, except for zinc. Al can improve corrosion resistance and strength of common brass. During the melting and casting process, bismuth can form compact oxide film for preventing melt oxidation, and for reducing the loss of zinc, which is prone to volatilize and oxidize. However, oxidation characteristics of aluminum are unfavorable for castability and weldability. In addition, aluminum will coarsen the grain of common brass. The zinc equivalent coefficient of aluminum is rather great, and can substantially enlarge the β phase zone. If combined with silicon, aluminum is prone to increase the β phase rate, and promote the formation of the γ phase. Therefore, it is beneficial for improving the cuttability of brass. The surface tension of aluminum (860 dyne / cm) is less than that of copper. It can form solid solutions in copper resulting in decreasing the surface tension of copper. It is favorable for spherifying bismuth, which is distributed in the grain boundary. The surface tension of zinc (760 dyne / cm) is less than that of copper. It can form solid solutions in copper. It is also favorable for spherifying bismuth which is distributed in the grain boundary. In this inventive alloy, aluminum content is lower than common commercialized aluminum brass, and is limited in the range of 0.3˜0.7 wt %, more preferably in the range of 0.4˜0.6 wt %. Higher aluminum content is not beneficial for castability and weldability.

Problems solved by technology

Therefore, such brass alloys cannot be used in the components for drinking water supply systems, such as faucets and valves.

With the increasingly extensive application of bismuth brasses, their negative effects are also increasingly notable, such as susceptibility to hot and cold cracking, poor weldability, the necessity to slowly heat and cool when annealing, etc.

The public casting bismuth brasses, such as C89550 (which comprises 0.6˜1.2 wt % Bi), have high tendencies to experience hot cracking during low pressure die casting, and are not easily welded.

However, antimony is more toxic than lead.

Antimony brass is not suitable for components used in drinking water supply system.

Most of them comprise small amounts of bismuth and the cost of raw material is rather higher.

Aluminum brass has good corrosion resistance, but its cuttability is inadequate.

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